Batu Tara, a tiny volcanic island in Indonesia’s Lesser Sunda Islands, released a plume of ash and/or steam in late April 2009. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image on April 30, 2009.

In this true-color picture, Batu Tara looks like a small, smoking speck in the Flores Sea. Initially blowing toward the northwest, the volcanic plume changes direction multiple times, forming a large question-mark shape, mingling with clouds in the north. When volcanic gases mingle with oxygen and moisture in the presence of sunlight, vog, or volcanic smog, often results. The off-white color and diffuse shape of the volcanic plume in the north are suggestive of vog.

Batu Tara is a stratovolcano composed of alternating layers of lava, ash, and rocks ejected by earlier eruptions. The volcanic island’s first historical eruption began in 1847. More recently, the volcano began a period of intermittent activity, producing repeated ash and steam plumes in 2007.